1. Field of the Invention
The present invention relates to lubricants, especially lubricating oils, and, more particularly, to a class of ashless and phosphorus-free, antiwear, anti-fatigue, and extreme pressure additives therefor derived from substituted linear thioureas.
2. Description of Related Art
In developing lubricants, there have been many attempts to provide additives that impart anti-fatigue, anti-wear, and extreme pressure properties thereto.
Zinc dialkyldithiophosphates (ZDDP) have been used in formulated oils as anti-wear additives for more than 50 years. However, zinc dialkyldithiophosphates give rise to ash, which contributes to particulate matter in automotive exhaust emissions. Regulatory agencies are seeking to reduce emissions of zinc into the environment. In addition, the phosphorus is also suspected of limiting the service life of the catalytic converters that are used on cars to reduce pollution. It is important to limit the particulate matter and pollution formed during engine use for toxicological and environmental reasons, but it is also important to maintain undiminished the anti-wear properties of the lubricating oil.
In view of the aformentioned shortcomings with the known zinc and phosphorus-containing additives, efforts have been made to provide lubricating oil additives that contain neither zinc nor phosphorus.
U.S. Pat. No. 5,935,913 discloses a composition comprising:
(A) a lubricant, and PA1 (B) at least one cyclic thiourea selected from the group consisting of: ##STR2##
wherein R.sub.1 and R.sub.2 are independently selected from the group consisting of alkyl, functionalized alkyl, and hydrogen.
Illustrative of non-zinc, i.e., ashless, non-phosphorus-containing lubricating oil additives are the reaction products of 2,5-dimercapto-1,3,4-thiadiazoles and unsaturated mono-, di-, and tri-glycerides of U.S. Pat. No. 5,512,190 and the dialkyl dithiocarbamate-derived organic ethers of U.S. Pat. No. 5,514,189.
U.S. Pat. No. 5,512,190 discloses an additive that provides antiwear properties to a lubricating oil. The additive is the reaction product of 2,5-dimercapto-1,3,4-thiadiazole and a mixture of unsaturated mono-, di-, and triglycerides. Also disclosed is a lubricating oil additive with antiwear properties produced by reacting a mixture of unsaturated mono-, di-, and triglycerides with diethanolamine to provide an intermediate reaction product and reacting the intermediate reaction product with 2,5-dimercapto-1,3,4 thiadiazole.
U.S. Pat. No. 5,514,189 discloses that dialkyl dithiocarbamate-derived organic ethers have been found to be effective antiwear/antioxidant additives for lubricants and fuels.
U.S. Pat. No. 5,498,809 discloses oil soluble copolymers derived from ethylene and 1-butene that have a number average molecular weight between about 1,500 and 7,500, at least about 30 percent of all polymer chains terminated with ethylvinylidene groups, and an ethylene-derived content of not greater than about 50 weight percent, and which form solutions in mineral oil free of polymer aggregates, as determined by light scattering measurements. Lubricating oil additives, particularly dispersants, produced by the functionalization and derivatization of these copolymers are said to have enhanced performance (e.g., improved dispersancy and pour point) in lubricating oil compositions, attributable in part to the combination of properties characterizing the copolymers.
U.S. Pat. Nos. 5,084,195 and 5,300,243 disclose N-acyl-thiourethane thioureas as antiwear additives specified for lubricants or hydraulic fluids.
U.S. Pat. No. 4,303,539 discloses thiocarbamyl derivatives, including thioureas and thiocarbamic esters derived from the reaction of an alkenyl isothiocyanate with an amine and alcohol or thio, respectively, have utility as an additive for hydrocarbons, particularly fuels and mineral lubricating oils whereby enhanced anticorrosion, oxidation inhibition and/or dispersancy activity is imparted to said hydrocarbons.
U.S. Pat. No. 4,263,154 discloses hydrocarbon-soluble sulfur-nitrogen compound resulting from the reaction of a dialkyl-4-hydroxy benzyl thiocyanate and a C.sub.12 -C.sub.24 alkyl primary amine which compounds have utility as multifunctional, i.e. antioxidation, antiwear, extreme pressure and lubricity modification, additive for fuels and lubricants.
The disclosures of the foregoing references are incorporated herein by reference in their entirety.